On Monday, Patrick W. thus responded:
Indeed.. Where does that construct come from?
> printf("'N' = %d <-> FALSE[\"NY\"] = %d\n", 'N', FALSE["NY"]);
I have never seend TRUE["NY"], and would have guessed cpp would change
it to 1["NY"] which doesn't mean anything to me. It appears to want to
be "NY"[1] ?! How come it works?
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I guess the example code requires some explaining:
In the first case, TRUE["NY"] expands to 1["NY"] which is semantically
interpreted as *(1 + "NY") and therefore computes to 'Y'.
Whereas in the second case, TRUE["NY"] expands to !FALSE["NY"] which in
turn expands to !0["NY"] .
That computes to !*(0 + "NY") simplified into !*"NY" or !'N' finally
resulting in the integer value 0.
Unbeknownst to the vast majority of C programmers, subscripting in C is
indeed commutative:
p[i] is the same as *(p + i) same as *(i + p) or i[p].
I've seen it used in obfuscated C code contest submissions, in C puzzles,
and similar teasing tests.
Enjoy,
Charlie Gordon,
The C teaser
